Dynamical effects in molecular junctions

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Michael Galperin of the University of California San Diego is supported by an award from the Theory, Models and Computational Methods program in the Chemistry Division to develop non-equilibrium many-body methods for calculating electron transport in molecular junctions. Both resonant and non-resonant inelastic electron scattering are of concern in molecular-scale electronics where a single molecule may form a current-carrying bridge between different parts of a nanoscale device. At the core of the work is the incorporation of molecular quantum states into transport formalisms based on Hubbard non-equilibrium Green functions and quantum master equations. This allows simultaneous consideration of coupling between a single molecule and electrodes, optical and plasmonic excitation and scattering, electronic transitions and charge transfer, and vibrations and heat transfer. A need for development of these capabilities comes from emerging experiments such as the simultaneous measurement of conductance and Raman scattering for molecules bridging metallic break junctions under an applied potential bias. Addition of a mixed classical-quantum approach allows accommodation of nonadiabatic molecular motion and switching. The drive toward ever-smaller electronic devices has as a limit the case of current traversing a single molecule that is attached to leads on either side. Usually current-carrying devices have so many atoms that they are treated statistically and not individually. If a single molecule forms a bridge this is no longer possible, and the electronic and vibrational motions of this molecule strongly affect the measured conductance and other properties. The work under this award develops a consistent theoretical picture joining the statistical treatment of the leads and the rigorous quantum treatment of the attached molecule. This project requires merging elements from several different disciplines, including quantum chemistry, molecular spectroscopy, transport theory and statistical physics. Molecular electronics courses for graduates and undergraduates will be developed that provide these interconnections in ways that traditional disciplinary courses cannot.